Cartwright studied Kenneth Parks, one of the most famous somnambulists of all time, who killed his mother-in-law in 1987 and was the inspiration for a television movie with Hillary Swank, "The Sleepwalking Killing."
Parks, a 23-year-old Toronto man with a wife and infant daughter, got in his car and drove 14 miles to the home of his in-laws. There, while still asleep, he stabbed to death the woman who called him the "gentle giant."

"He adored her," said Cartwright.

Afterward, Parks drove to the police station and declared, "I think I have killed some people...my hands." Later, doctors repaired several cut flexor tendons in his hands. A jury later found him not guilty.

"He still writes to me when he is in trouble," said Cartwright, who interviewed Parks in prison and later wrote about him in the journal Sleep. "He is the sweetest guy in the world."

What can go wrong when the brain is asleep is the topic of a chapter in Cartwright's latest book, "The 24-Hour Mind," due out in May. Filmmaker Allen Wolf also explores the topic in a fictional film inspired by Parks' case and others, "In My Sleep," which premieres in Los Angeles and New York this month.

A psychological thriller, the story opens when a man awakens in the middle of a cemetery, half-naked, with no idea how he got there.

To sleep experts, some of whom Wolf consulted for the medical dialogue, the narrative is not so far-fetched.

The topic of sleepwalking still fascinates more than a century after socialite Albert Jackson Tirrell was the first American to successfully use the sleepwalking defense after killing a Boston prostitute in 1846.

Sleepwalking is relatively common in childhood, but can be troublesome if it persists in adulthood.

About 15 to 20 percent of all children, both girls and boys, sleepwalk, according to the American Sleep Association. Usually it peaks around age 11 or 12 and rarely continues as they mature.

"Usually little kids get up and walk and you try to bring them back to bed and comfort them and make sure they are not wandering in to danger," said Cartwright. "But they can beat you up with their little fists."

Such was the case with Sue Sullivan's 13-year-old son Stephen, who has had always had night terrors.

"My son has been to 'walk the dog," and to "get the mail' and other interesting actions when sleeping," said the 46-year-old salesperson from Rochester, N.Y.

But one night it turned violent.

"I woke up to him screaming and punching me and pulling my hair," she said. "He was 'beating up the bad guy, Mom.' But in reality I was the one who he was beating up."

He has since been in a sleep study and is taking medication, which hasn't stopped the sleepwalking, but has stemmed the aggression.